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BQ76940EVM - Significance of TVS Diodes (D22,D23 & D24)

Girish Gangadharaiah
Intellectual 515 points
Other Parts Discussed in Thread: BQ76940

Hey Everyone,

I wanted to use BQ7940 in my design, so want to understand few things, So I observed in SCHEMATICs of BQ76940EVM that TVS diode (D22,D23 & D24) are used. I just wanted to know the significance of these diodes. 

Please help me understand the same.

I am not able to attach the SCHEMATIC, It is available at " http://www.ti.com/lit/ug/slvu925b/slvu925b.pdf " 

  • 0
    TI__Expert 6085 points
    D22/D23/D24 are NOT transient voltage suppressor; they are blocking diodes. The respective diodes protect the power sources, VBAT,VC5X, VC10X. They they can also help during random cell connection , as the BAT comes up slower than VC5X. get forward biased during early portion of device power-up. The max voltage between top cell input and the BAT pin or top Vcx pin and its power pin 7V. A diode should be used between the top VCx pin of each group for the bq76940.
  • 0 in reply to Vish Nadarajah
    Intellectual 515 points

    Hey Vish, Sorry for confusion. Yes they are blocking diodes.

    But since they were used between VC5-VC5X, VC10-VC10X & VC15-BAT.
    Why do we need 100V diode there, It should have been with Lesser Voltage rating right?
    And
    Can we use Schottky diode or other type of diode in this place?

  • 0 in reply to Girish Gangadharaiah
    TI__Expert 6085 points

    The diodes (VC5-VC5X), (VC10-VC10X), (VC15-VBAT),  are called ground power diodes as explained in SLUA749 fig 20. 

    These need to be conventional diode. The pp19-22 give a great write-up of the benefits.